The present invention relates to a permanent magnet, more particularly, to a manganese-aluminum-carbon (Mn-Al-C) alloy magnet containing copper (Cu) in order to improve plasticity thereof.
An alloy comprising manganese, aluminum and carbon in suitable amounts and having been subjected to suitable heat treatment is a known permanent magnet material. Recently, a new alloy magnet comprising 68.0 to 73.0% by weight of manganese, carbon in amounts ranging from (1/10 Mn -- 6.6) to (1/3 Mn -- 22.2)% (wherein Mn in the formulae represents percent of manganese content) and the remainder aluminum and having been subjected to warm plastic deformation has been disclosed in U.S. Pat. No. 3,976,519. The new magnet, subjected to warm plastic deformation, exhibits excellent magnetic characteristics, e.g. the (BH)max is several times as large as that of the magnet subjected to suitable heat treatment, and is machinable. The permanent magnet subjected to warm plastic deformation is useful for practical purposes and is produced industrially.
However, some difficulties have been encountered in the warm plastic deformation step during industrial manufacture of this magnet, as follows: the Mn-Al-C ternary alloy exhibits plasticity at a temperature of more than 530.degree. C. and can be subjected to warm plastic deformation, for example, extrusion or die-upsetting. But the plasticity of the ternary alloy is not very good, that is to say deformation resistance of the ternary alloy is not very small, and therefore the ternary alloy is subjected to deforming by applying a larger pressure and to deforming under higher temperature, which yields lower deformation resistance. But the application of a large pressure at the deformation step brings about a remarkable shortening of life of a die because of abrasion and creep, and brings about cracks within the deformed alloy magnet. The high deformation temperature also brings about shortening of life of the die because of decrease of the mechanical strength thereof and further induces decrease of the magnetic characteristics of the deformed alloy. Then, the large deformation pressure and the high deformative temperature result in increase of energy cost and manufacturing equipment cost, because a particular die built from a particular material and a complicated structure and press with large pressure capacity are required. These difficulties can be solved, if deformation resistance of the alloy magnet is decreased. For example, the life of a die is almost proportional to the exponent of the decreasing coefficient of the deformation resistance. When using a die composed of a tungsten-cobalt-cromium alloy steel, when the deformation resistance of the Mn-Al-C alloy is decreased by 10%, the life-time of the die is extended approximately ten fold.
In order to solve the above-mentioned difficulties in the industrial production, it has been strongly desired to improve the plasticity of the Mn-Al-C ternary alloy, that is to say, to decrease the deformation resistance of the ternary alloy.